Natural Selection Image Map


Depletion of Natural Resources

Poor Farming Practices

Mayan farming.  Ancient Mayans in Central America (from about 0 to 900 AD) had a "slash and burn" method of farming. Each year after the harvest, they would cut down all the old plants and set the fields afire. Then they would repeat the process again the next year on the same plot of ground. After about 7 years, the soil was so depleted of nutrients and organic matter that it had to be abandoned. They moved on to clear another patch of ground.

Burning crop land depletes the soil and exposes it to wind and rain erosion

The Mayan population grew, sometimes to include cities with a hundred thousand or more people. Soon, the farmers could not grow enough food and there was no more good soil. Then the farmers started farming marginal land, such as hillsides. That created other problems, because the hillsides were easily eroded by rain. We may never know all the reasons why the Mayan civilization disappeared, more or less suddenly around 900 AD.  Two things are clear: 1) people abandoned the cities and returned to simpler living, and 2) massive farming efforts could no longer be sustained.

Oklahoma Dust Bowl.  In the 1930s in the U.S., most of Oklahoma and much of West Texas turned into a dust bowl because of a drought. 

Trees were cut down and grassland was turned into crop land. The soil then became exposed to erosion from rain and wind.  When drought came, the land became worthless, unable to grow anything. The air was choked with dust. Many farmers had to abandon the land and move to other states, such as California.  Click here to read the story of the Dust Bowl.


People who live on islands are very dependent on the fish life around them. As an island becomes more populated with people, the demand for food from the sea can outstrip the source. 

This has happened recently on the islands off the coast of Honduras. The people there are very poor. Their struggles were only made worse when they depleted the fish and sea creatures. Such problems were made even worse when a seafood restaurant chain set up a factory there for processing lobster and fish. It didn't take long to exhaust the sea's supply.  

Coral reefs shelter and feed many fish.

Where did all the fish go?

Over-fishing not only threatens the human food supply but also that of other species that feed on sea life. One example of a species threatened in this way is the Russian Brown bear.

One hopeful sign is fish farming, where genetically modified fish are raised in captivity. Click here for more on the promise of fish farming. For more on the world crisis in over-fishing, click here.

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